<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <div class="box" style="background-color:red;color:white">
    我是box
  </div>

  <script>
    var boxEl = document.querySelector('.box')
    console.log(boxEl.style)
    console.log(boxEl.style.backgroundColor)

    // 设置为空字符串 则为默认样式
    boxEl.style.display = ""
    boxEl.style.fontSize = ""
    // 会覆盖掉原来的style
    boxEl.style.cssText = "font-size:30px; color:orange"
  </script>
</body>

</html>